Particle chromatography, called Cascadography, operates in a manner similar to all the chromatographs. The sample is injected, as a pulse, into the system and is immediately carried into a sorption column or stack where the particles move from one "plate" to the next. In moving from "plate" to "plate" the speed is governed by the individual particle's characteristics. After the particles exit the stack, they encounter a detector which measures the particles. A recording is made of the stack output as a function of time. If there exists in the sample a group of particles with identical or very nearly the same characteristics, then the output recording will show a pulse or peak.
The great bulk of material handled in industry is in the particulate or powder form, yet, to date, most of the analytical, research, experimental and development work has been done on fluids. Since fluids are more uniform in nature, far easier to characterize and to analyze, it is not surprising that fluid chromatographs would be in the most advanced state of development. Because of the extraordinary industrial importance of powders, any theoretical or instrumental breakthroughs in the powder field is important from both the scientific and economic viewpoint. Cascadography, because of its ease in characterizing powders, is this type of breakthrough.
Particle characterization has come slowly to the powder field because, unlike molecules, each particle in the universe is unique. Cascadography is a sophisticated concept for the powder field and was developed specifically to characterize powders. A quantitative method, called Fourier Grain Analysis or Morphological Analysis, of measuring the shape of individual particles, has been extended to measuring the shape mix in powders, when it is desired to know if two powders samples are from the same or a different source. For a given size of particle, this method requires that the shape of two hundred particles be measured in each sample and then, using clustering theory in hyperspace, a comparison is made between the two powders to see if there is a significant difference between the two shape mixes to confirm that the powders come from different sources.
While Morphological Analysis is a powerful, sophisticated research technique of great promise, it neither separates the particles into discrete batches, nor does it survey the entire sample. In short, it does not characterize the powder. However, cascadography, like sieving, is both easy to do and easy to understand. By temporally separating particles, Cascadography characterizes powders in a new dimension, residence-time-shape. This form of characterization is immediately applicable to industrial problems as diverse as the grading of grains, wheat and corn, as well as the characterizing of abrasives.
One separation unit operation never successfully modeled is sieving. To successfully model any unit operation, one must know both the characteristics of the feed and the selectivity function of the unit operation. Particles of different shape, even though their "size" is the same, will pass through a sieve at different rates. Yet Jansen et. al. showed that the sieving of mono size spheres obeys an exponential decay law for the number of spheres remaining on a sieve. Obviously the feed for normal size distribution consists not only of variations in particle size, but also of particle shape. As has been shown by Roberts and Beddow, these shape variations effect the rate at which particles progress through the sieve. Until now, no one has either characterized the feed to a sieve, any other sizing device, or even suggested a method for doing so. This invention presents a method, called Sieve Cascadography, and an apparatus called a CASCADEOGRAPH that will characterize the feed to a sieve or industrial screen.
Consider now several unsolved industrial problems, one on grain grading and the other on abrasive evaluation and quality control. Since there are no instrumental methods of grading food grain, it is done by humans, resulting in an expensive, judgemental and corruptible system, as is reported in the press from time to time. Needed is a method to measure the amount of whole grain, cracked grain, filth, chaff and adulterants in a sample. Cracked grain is elongated and smaller than whole grain, chaff is very elongate, rat or mouse boluses are smooth and ellipsoidal, and finally adulterants may have any shape-size. Each of these particles will have their own residence time characteristics on a sieve and thus will report at a different time to the cascadograph product. Just by looking at the output of the cascadograph one can quantitatively tell the ratio of whole to cracked corn, the amount of filth and chaff, and if there is an unusual peak or profile, the amount of adulterant.
In the abrasive industry there are two useful particle shapes, triangles and blocks, in addition, there are useless shapes such as plates. Triangular particles are useful in the making of grinding wheels, while blocky particles are good for grits and abrasive sheets. If one is manufacturing or buying an abrasive one wants to know the particle shape content but at present there is no satisfactory way of profiling the abrasives shape mix. Since each shape particle, for a narrow size range, has a characteristic residence time on a sieve, Sieve Cascadography is an ideal method of assaying the shape profile of an abrasive sample. Both buyer and vendor can agree on the specification and simple tests can be made to determine if the sample meets the specification.